Ophthalmologic apparatus

ABSTRACT

An opthalmologic apparatus is disclosed. In one aspect, the apparatus includes an ocular fundus photographing systems for forming an ocular fundus image of the examined eye, based on a reflective beam from the ocular fundus of the examined eye, and an ocular fundus tracking controller for detecting a gaze direction of the examined eye by receiving the reflective beam reflected at a reflective region of an illumination region illuminated on the ocular fundus and for tracking the ocular fundus based on the detection results of the gaze direction. The ocular fundus tracking controller may include scanning mirrors for scanning an area to detect a reflective beam from the ocular fundus, tracking mirrors for controlling tracking to the ocular fundus, an objective lens disposed opposite to the examined, and an offset mirror M 19  for adjusting a detection axis in a gaze direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application has related subject matter to U.S. application Ser. No.______ (Attorney Docket No. CREO2.002AUS) filed on the same date. Thisapplication claims priority from Japanese Patent Application No.2006-172769, filed with the Japanese Patent Office on Jun. 22, 2006, thecontents of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an opthalmologic apparatus thatincludes an ocular fundus tracking controller for detecting a directionof gaze of an examined eye and following an ocular fundus imaging systemin the direction of gaze, thereby photographing an ocular fundus withhigh resolution.

2. Description of the Related Technology

A conventional ocular fundus camera produces a deterioration in anocular fundus image photographed because of optical aberration owned bythe tested eye. Accordingly, the ocular fundus camera has a disadvantagethat an clear image of the ocular fundus having high magnificationcannot be obtained.

Owing to this, these days, a technology for photographing an ocularfundus image is proposed by which the optical aberration of the testedeye is measured and compensated by using a compensation optical systembased on the measured results. The technology can eliminate an influencecaused by the optical aberration of the tested eye to produce a highermagnification of the ocular fundus image compared with the conventionaltechnique.

However, the conventional opthalmologic apparatus has difficulties inphotographing an ocular fundus image with much higher magnification andhigher resolution applied to a visual cell level. One of thedifficulties is a fixation micro-movement of an eyeball. That is, theeyeball always continues a micro-movement called a fixationmicro-movement, which always moves a gaze direction of the eye.Accordingly, since an ocular fundus image to be photographed isoscillating and causes a blur, it is essential to remove an influence ofthe fixation micro-movement in order to take a picture of the ocularfundus image with much higher resolution.

So as to get rid of the blur of the ocular fundus image in a differenceof the gaze direction of the eye, an opthalmologic apparatus has beenproposed in which the gaze direction of the examined eye is detected andtracking is carried out with respect to the ocular fundus based on thedetection results. See, for example, U.S. Pat. No. 5,943,115.

According to the technology disclosed in the US patent, in order todetect a gaze direction of the tested eye on the ocular fundus, adetection beam of a infinitesimal region close to the point light sourceis projected to the ocular fundus for scanning so that a circular locusis drawn on the ocular fundus. A reflective beam at the ocular fundus ofthe detection beam is received to detect the gaze direction of thetested eye, which controls a pair of tracking mirror from.

The optical system projects a detection beam on the ocular fundus of theexamined eye through the order of a detection light source, a vibrationreflective mirror (scanning mirror) for scanning the detection beam in acircular locus on the ocular fundus, a tracking mirror for controllingtracking according to the gaze direction of the examined eye that isdetected, and an objective lens. Then, the optical system receives areflective beam from the ocular fundus via the objective lens, thevibration reflective mirror (scanning mirror) and the tracking mirror.

On the other hand, an area to which a detection beam is projected and atwhich a reflective beam is detected may be a characteristic portionbrighter than the environment, for example, an optic disc. Since adesired region of the ocular fundus other than the characteristicportion should be photographed, projection of the detection beam andshift of the axis of the light receiving system (corresponding to thedetection axis of the gaze direction) are arbitrarily adjusted withrespect to the optical axis for photographing the ocular fundus.

Because of this, the US patent discloses a structure in which thedetection optical axis of the vibration reflection mirror (scanningmirror) to scan the detection beam is shifted by a predetermined amountto shift the detection axis of the gaze direction.

If the technology of the US patent is applied to an opthalmologicapparatus having high magnification, the detection axis of the gazedirection can be shifted in the high magnification observation region.However, when shifting the detection axis of the gaze direction outsidethe observation region, there is a disadvantage that an effectiveaperture of the ocular fundus high magnification should be much higherthan is necessary. There is a need for a opthalmologic apparatus thatcan solve the disadvantage.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

Aspects of the invention provide an opthalmologic apparatus thatsatisfies the need. Certain aspects include an opthalmologic apparatusthat can adjust a detection optical axis in the gaze direction to alarge extent and even to outside a region of ocular fundus highmagnification observation, and photograph the ocular fundus with highmagnification and high resolution, although an effective aperture of aphotographing lens for the ocular fundus high magnification observation.

One aspect is an opthalmologic apparatus comprises an ocular fundusphotographing system that forms an image of an ocular fundus of a testedeye on a photographing apparatus based on a reflective beam from theocular fundus; and an ocular fundus tracking controller that detects alight beam from the ocular fundus, reflected at a reflective region ofan illuminated region on the ocular fundus to detect a gaze direction ofthe tested eye, and performs tracking with respect to the ocular fundusbased on the detection result of the gaze direction. The ocular fundustracking controller comprises a scanning mirror for scanning an area onwhich a detection beam projected on the ocular fundus is detected or areflective beam from the ocular fundus is detected; a tracking mirrorfor controlling tracking to the ocular fundus; an objective lensdisposed opposite to the tested eye; and an offset mirror positionedbetween the objective lens and the tracking mirror outside of aphotographing optical path for the ocular fundus, for adjusting adetection axis of the gaze direction.

The reflective beam from the ocular fundus may proceed to thephotographing apparatus not through the offset mirror after entering thetracking mirror.

The ocular fundus photographing system may include a compensationoptical system for compensating optical aberration of the tested eye.

An opthalmologic apparatus may further comprise an illumination beam forphotographing the ocular fundus and a detection beam for detecting thegaze direction of the tested eye, the illumination beam having awavelength that is different from that of the detection beam.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings.

FIG. 1 is a block diagram illustrating an opthalmologic apparatus inaccordance with an embodiment the present invention.

FIG. 2 is a detailed view illustrating an optical system of theopthalmologic apparatus shown in FIG. 1.

FIG. 3 is an illustrative view of an ocular fundus of a tested eye inFIG. 1.

FIG. 4A is an illustrative view of an optical path showing an offset foran ocular fundus photographing beam and a detection beam, where trackingcontrol is explained for the ocular fundus of the tested eye shown inFIG. 1.

FIG. 4B is an illustrative view of a locked state in which a trackingtarget is locked owing to tracking by using a pinhole correspondingregion.

FIG. 4C is an illustrative view of a state in which the tracking targetto be detected by the pinhole corresponding region is shifted to theright.

FIG. 4D is an illustrative view of a state in which the tracking targetto be detected by the pinhole corresponding region is unlocked.

FIG. 5A is an illustrative view of a state in which the tracking targetto be detected by the detection beam is shifted to the right, where theprinciple of locking operation for the tracking target in the ocularfundus shown in FIGS. 4A to 4D is explained.

FIG. 5B is an illustrative view of a state in which the tracking targetto be detected by the detection beam is locked by tracking.

FIG. 5C is an illustrative view of a state in which the tracking targetto be detected by the detection beam is shifted to the right (out oflock).

FIG. 6 is an illustrative view of the ocular fundus photographing imageof the tested eye shown in FIG. 1.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

Embodiments of an opthalmologic apparatus in accordance with the presentinvention will be discussed referring to the drawings.

FIG. 1 is a block diagram illustrating an opthalmologic apparatus inaccordance with the present invention. The opthalmologic apparatusincludes a low magnification ocular fundus photographing system 1 forobserving an ocular fundus Ef of the examined eye E, a highmagnification ocular fundus photographing system 2 for photographing theocular fundus Ef of the examined eye E, an ocular fundus trackingcontroller 3 for following the high magnification ocular fundusphotographing system 2 to the gaze direction of the examined eye E, anda photographic portion selector 4 for selecting a photographic portion.

FIG. 2 is a detailed view illustrating an optical system of theopthalmologic apparatus shown in FIG. 1. The optical system includes anobject lens Ob positioned in front of the tested eye E, the lowmagnification ocular fundus photographing system 1, the highmagnification ocular fundus photographing system 2, an anterior eyesegment observation system 5, an alignment detection system 6, afixation target projection system 7, a wave front aberrationcompensation system 8, an ocular fundus tracking control driver 9, and atracking detector 10.

Anterior Eye Segment Observation System 5

The anterior eye segment observation system 5 includes an anterior eyesegment illumination source (not shown) for illuminating an anterior eyesegment of the tested eye E and an anterior eye segment observationcamera Ca1. Between the anterior eye segment of the tested eye E and theanterior eye segment observation camera Ca1, there exist an objectivelens Ob, a half mirror M1, wavelength selection mirrors M2 and M3, and atotal reflection mirror M4.

The anterior eye segment illumination source has wavelength λ=700 nmthat is used as an anterior eye segment illumination light. The halfmirror M1 reflects half of the light beams of wavelength 700 nm andtransmits half of the light beams, respectively. The wavelengthselection mirror M2 transmits all of the light beams from λ=700 nm to770 nm, and reflects the light beams from λ=500 nm to 700 nm and fromλ=800 nm to 1100 nm. The wavelength selection mirror M3 transmits halfof the light beams of wavelength λ=770 nm and reflects half of the lightbeams, and transmits all of the light beams λ=700 nm.

The anterior eye segment illumination light beams are reflected at theanterior eye segment, focused by the object lens Ob, and led to the halfmirror M1. Then, the anterior eye segment illumination light beams aredeflected toward the wave selection mirror M2 by the half mirror M1,transmit through the wave selection mirrors M2 and M3, and are led tothe total reflection mirror M4. Moreover, the anterior eye segmentillumination light beams are led to the anterior eye segment observationcamera Ca1 by the total reflection mirror M4, in which an anterior eyesegment image of the tested eye E is formed.

While an observer or photographer observes, on a monitor, the anterioreye segment image focused in the anterior eye segment observation cameraCa1, he moves the opthalmologic apparatus by a manual operation toperform an alignment of the apparatus itself with respect to the testedeye E.

Alignment Detection System 6

The alignment detection system 6 includes an X-Y alignment detectionlight source Os1, an alignment mirror M5, an X-Y alignment sensor Se1, aZ alignment detection light source Os2, and a Z alignment sensor Se2.

Between the half mirror M1 and the alignment mirror M5, there exists amirror M6 having a hole h0 therein. The alignment mirror M5 totallyreflects the light beam of wavelength λ=770 nm, and totally transmitsthe light beams below wavelength λ=700 nm and over wavelength λ=800 nm.

LED's of wavelength λ=770 nm are used as the X-Y alignment detectionlight source Os1 and the Z alignment detection light source Os2. PSD's(semiconductor position detector) are used as the X-Y alignment sensorSe1 and the Z alignment sensor Se2.

A X-Y alignment detection light beam from the X-Y alignment detectionlight source Os1 is reflected by the alignment mirror M5 to pass throughthe hole ho. Then, the X-Y alignment detection light beam proceeds tothe half mirror M1 and the objective lens Ob to be led to a cornea C ofthe tested eye as a parallel light flux. A bright spot image (falseimage) is formed on the cornea C by the cornea reflection of the X-Yalignment detection light beam.

The X-Y alignment detection light beam reflected by the cornea C is halfreflected by the half mirror M1 to reach the wavelength selection mirrorM2. Then, the X-Y alignment detection light beam totally transmits thewavelength selection mirror M2 to be led to the wave selection mirrorM3, which reflects a part of the X-Y alignment detection light beam tothe X-Y alignment sensor Se1 and transmits the rest to the totalreflective mirror M4.

The X-Y alignment sensor Se1 detects a positional difference in the X-Ydirection with respect to the apparatus itself in a plane vertical to anoptical axis of the object lens Ob, based on the position of the brightspot image formed on the cornea C of the tested eye E, where the Xdirection is defined as the left and right direction and Y direction isdefined as the upward and downward direction with respect to the testedeye E.

The Z alignment detection light beam from the Z alignment detectionlight source Os2 is projected to the cornea C of the tested eye E from adiagonal direction. A bright spot image (virtual image) is formed on thecornea C owing to cornea reflection of the Z alignment detection lightbeam. The Z alignment detection light beam is reflected in the diagonaldirection by the cornea C to arrive at the Z alignment sensor Se2. The Zalignment sensor Se2 detects a positional difference (in the opticalaxis direction of the object lens Ob) in the Z axis direction withrespect to the apparatus itself of the tested eye E, based on theposition of the bright spot image formed on the cornea C.

The alignment detection system 6 is used to automatically perform aprecise alignment of the apparatus itself with respect to the tested eyeE after a rough alignment of the apparatus itself with respect to thetested eye E is completed according to the anterior eye segmentobservation system 5.

Since the principle of alignment for the alignment detection system 6 ispublicly well-known, the detailed explanation of the principle isomitted.

Low Magnification Ocular Fundus Photographing System 1

The low magnification ocular fundus photographing system 1 includes alow magnification photographing illumination light source (for example,a halogen lamp) Os3, a wavelength selection mirror 7, a lowmagnification photographing diopter compensation lens L1, a waveselection mirror M8, a total reflection mirror M9, and a lowmagnification photographing camera (mono-chrome camera) Ca2.

The low magnification photographing diopter compensation lens L1, movedbackward and forward along the optical axis O1, is used for compensatinga refractive error of an eyeball.

The wavelength selection mirror (dichroic mirror) M7 wholly transmitsthe light beam over wavelength λ=800 nm, and totally reflects the lightbeam between λ=500 nm and 700 nm. The wavelength selection mirror M7 isalso used for a high magnification photographing illumination lightsource Os4. The wavelength selection mirror M8 totally reflects thelight beam below wavelength λ=800 nm and wholly transmits the light beamover wavelength λ=800 nm.

Light of infrared component above wavelength λ=860 nm is used as a lowmagnification photographing illumination light beam. The light beam ofthe infrared component totally passes through the wavelength selectionmirror M7 to reach the hole-made mirror M6, by which the light beam isreflected to the half mirror M1. Moreover, the light beam, aftertransmitting the half mirror M1, is condensed by the object lens Ob tobe led to the ocular fundus Ef of the tested eye E as a annularillumination light flux, in which the ocular fundus Ef of the tested eyeE is illuminated.

The illumination light beam reflected by the ocular fundus Ef isconverged by the object lens Ob to pass through the half mirror M1 andthe hole h0 of the hole-made mirror M6. Then, the illumination lightbeam is led to the low magnification photographing diopter compensationlens L1 by way of the alignment mirror M5. After the refractive error ofthe eyeball is compensated by the low magnification photographingdiopter compensation lens L1, the illumination light beam is led to thetotal reflection mirror M9 through the wave selection mirror M8. Afterthis, the illumination light beam is deflected to the low magnificationphotographing camera Ca2 by the total reflection mirror M9, by which animage of the low magnified ocular fundus is focused in the lowmagnification photographing camera Ca2.

The low magnification ocular fundus photographing system 1, which is anoptical system that corresponds to a conventional ocular fundus camera,is used for observing the ocular fundus Ef in a wide visual field andfor determining a photographing position when photographing the ocularfundus at high magnification.

Fixation Target Projection System 7

The fixation target projection system 7 includes a fixation light sourceOs5 and the wavelength selection mirror M8. The fixation light sourceOs5 is an LED that emits light of wavelength λ=560 nm. The fixationtarget light from the fixation light source Os5 is deflected to the lowmagnification photographing diopter compensation lens L1 by thewavelength selection mirror M8 to be led to the object lens Ob throughthe low magnification photographing diopter compensation lens L1, thealignment mirror M5, the hole ho of the hole-made mirror M6, and thehalf mirror M1. The objective lens Ob forms a light source image of thefixation target on the ocular fundus Ef. The examinee pays closeattention to the fixation target. The gaze direction of the examined eyeE is determined by the fixation target projection system 7.

The fixation light source Os5 is movably constructed in a planeperpendicular to the optical axis 02. Changing the gaze direction of theexamined eye E by moving the fixation light source Os5 enables the lowmagnification ocular fundus photographing system 1 and the highmagnification ocular fundus photographing system 2 to observe apredetermined position of the ocular fundus.

Wave Front Aberration Compensation System 8

The wave front aberration compensation system 8 includes a projectionsystem and a light receiving system.

The projection system includes a wave front sensor light source Os6, ahalf mirror M10, a total reflection mirror M11, a wavelength selectionmirror 12, a wave front compensation element (for example, a reflectivetype of deformable mirror) M12′, an astigmatism compensation variablecross-cylinder Vcc, a wavelength selection mirror M13, a Y directiontracking mirror YTM1, an X direction tracking mirror XTM1, a wavelengthselection mirror M14, a total reflection mirror M15, a wavelengthselection mirror M16, and a high magnification photographing dioptercompensation mirror M17. An optical element of one portion of the wavefront aberration compensation system 8 is positioned in a optical pathof the high magnification ocular fundus photographing system 2 to beused with an optical element of the high magnification ocular fundusphotographing system 2.

The wave front sensor light source Os6 is used to illuminate a lightbeam of wavelength λ=830 nm to the ocular fundus Ef of the tested eye E.The half mirror has the characteristics of half transmittance and halfreflection. The wavelength selection mirror M12 totally transmits lightabove wavelength λ=800 nm, and totally reflects light below wavelengthλ=800 nm.

The astigmatism compensation variable cross-cylinder Vcc plays a role ofcompensating a spherical power, a cylindrical power, and an axis angle.The wavelength selection mirror M13 totally transmits light abovewavelength λ=860 nm, and totally reflects light below wavelength λ=860nm.

The wavelength selection mirror M14 totally transmits light abovewavelength λ=860 nm, and totally reflects light below wavelength λ=860nm. The wavelength selection mirror M16 totally transmits light abovewavelength λ=860 nm, and totally reflects light below wavelength λ=860nm, too.

A light beam of wavelength λ=830 emitted from the wave front sensorlight source Os6 is reflected by the half mirror M10 to reach the totalreflection mirror M11, which, in turn, reflects the light beam to thewavelength selection mirror M12. After passing through the wavelengthselection mirror M12, the light beam of wavelength λ=830 reaches thewavelength selection mirror M13 via the wave front compensation elementM12′ and the astigmatism compensation variable cross-cylinder Vcc.

The light beam of wavelength λ=830 is reflected by the wavelengthselection mirror M13 to arrive at the wavelength selection mirror M14 byway of the Y direction tracking mirror YTM1 and the X direction trackingmirror XTM1. Furthermore, the light beam of wavelength λ=830 isreflected by the wavelength selection mirror M14 to hit against thetotal reflection mirror M15, which sends out the light beam to thewavelength selection mirror M16.

The light beam of wavelength λ=830 is totally reflected by thewavelength selection mirror M16 to reach the objective lens through thehigh magnification photographing diopter compensation mirror M17, thewavelength selection mirror M2, and the half mirror M1. The objectivelens projects a point light source image to the ocular fundus.

The light receiving system includes the half mirror M10, the totalreflective mirror 11, the wavelength selection mirror M12, the wavefront compensation element (deformable mirror) M12′, the astigmatismcompensation variable cross-cylinder Vcc, the wavelength selectionmirror M13, the Y direction tracking mirror YTM1, the X directiontracking mirror XTM1, the wavelength selection mirror M14, the totalreflection mirror M15, the wavelength selection mirror M16, a highmagnification photographing diopter compensation mirror M17, and a wavefront sensor Se3.

The wave front sensor Se3 includes a Hartmann's diaphragm having anaperture with numerous holes and a light receiver for detecting aposition reached by each beam that has passed through the numerousholes. The wave front is detected based on the reached position by thebeam on the light receiver of the wave front sensor Se3. The wave frontsensor Se3 is publicly known.

The reflective light beam from the ocular fundus takes a reverse lightpath, that is, the reflective light beam passes through the objectivelens, the half mirror M2, the wavelength selection mirror M2, the highmagnification photographing diopter compensation mirror M17, thewavelength selection mirror M16, the total reflection mirror M15, thewavelength selection mirror M14, the X direction tracking mirror XTM1,the Y direction tracking mirror YTM1, the wavelength selection mirrorM13, the astigmatism compensation variable cross-cylinder Vcc, the wavefront compensation element M12′, the wavelength selection mirror M12,and the total reflection mirror M11 to reach the half mirror M10,through which the reflective light beam is led to the wave front sensorSe3.

The wave aberration includes aberration caused by the tested eye. Theaberration measured by the wave front sensor Se3 controls the wave frontcompensation element M12′ to change its shape of the reflective surface.This compensates the wave aberration to compensate optical aberration ofthe tested eye.

For example, the opthalmologic apparatus in the prior art can take apicture of a cell about 5 μm in size. On the other hand, theopthalmologic apparatus in accordance with the present invention canphotograph a cell about 2 μm in size.

Since there is a limit in compensation quantity of the wave frontaberration the wave front compensation element M12′ can perform, thehigh magnification photographing diopter compensation mirror M17 ismoved in the direction of an arrow F-F to adjust an optical path fromthe wave front sensor Se3 to the ocular fundus Ef of the tested eye.This compensates most of the component of the spherical power(components of hyperopia and myopia) of refractive error of the testedeye E.

Rotational adjustment of a relative angle of a pair of cylindrical lensconstituting the astigmatism compensation variable cross-cylinder Vccand an overall angle compensates most of the astigmatism component ofrefractive error of the tested eye E.

High-degree aberration of aberration caused by refractive error of aneye ball cannot be removed by the high magnification photographingdiopter compensation mirror M17 and the astigmatism compensationvariable cross-cylinder Vcc. However, the high-degree aberration can becompensated by the wave front compensation element M12′. The wave frontaberration compensation system 8 can eliminate all types of aberrationexcept for color aberration and distortion aberration to produce a clearimage even at higher magnification.

The X direction tracking mirror XTM1 and the Y direction tracking mirrorYTM1 constitute the ocular fundus tracking control driver 9.

High Magnification Ocular Fundus Photographing System 2

The high magnification ocular fundus photographing system 2 is composedof an illumination system and an image receiving system. Theillumination system includes the high magnification photographingillumination light source Os4 and the wavelength mirror M7.

The optical path of the image receiving system includes the wave frontaberration compensation system 8 and the ocular fundus tracking controldriver 9. The image receiving system includes a high magnificationphotographing camera Ca3 as a photographing device, an the image forminglens L2, the wavelength selection mirror M12, the wave frontcompensation element (deformable mirror) M12′, the astigmatismcompensation variable cross-cylinder Vcc, the wavelength selectionmirror M13, the Y direction tracking mirror YTM1, the X directiontracking mirror XTM1, the wavelength selection mirror M14, the totalreflection mirror M15, the wavelength selection mirror M16, the highmagnification photographing diopter compensation mirror M17. A color CCDcamera is used as the high magnification photographing camera Ca3.

A xenon lamp, for example, is used as the high magnificationphotographing illumination light source Os4. Light of wavelength λ=500nm to 700 nm from the xenon lamp is used as the high magnificationphotographing illumination beam. The illumination beam of wavelengthλ=500 nm to 700 nm from the xenon lamp is totally reflected by thewavelength selection mirror M7 to reach the hole-made mirror M6, bywhich the illumination beam is deflected. Then, the deflectedillumination beam hits against the ocular fundus Ef of the tested eye asan annular light beam, by way of the half mirror M1 and the objectivelens Ob.

The reflected illumination beam from the ocular fundus Ef is convergedby the objective lens Ob and reflected to the wavelength selectionmirror M2 via the half mirror M1. The illumination beam, which reachedthe wavelength selection mirror M2, proceeds to the high magnificationphotographing diopter compensation mirror M17, the wavelength selectionmirror M16, the total reflection mirror M15, the wavelength selectionmirror M14, the X direction tracking mirror XTM1, the Y directiontracking mirror YTM1, the wavelength selection mirror M13, theastigmatism compensation variable cross-cylinder Vcc, the wave frontcompensation element (deformable mirror) M12′, and the wavelengthselection mirror M12. Moreover, the illumination light is totallyreflected by the wavelength selection mirror M12 to be led to the imageforming lens L2, which enables magnification conversion by anelectrically movable revolver. The illumination light reflected at theocular fundus Ef is focused on a photographing surface of the highmagnification photographing camera Ca3 through the image forming lensL2.

Ocular Fundus Tracking Control Driver 9

The ocular fundus tracking control driver 9, which shares a part thereofwith a tracking detector 10, is used to dispose a photographic visualfield of the high magnification ocular fundus photographing system 2 ata predetermined position of the ocular fundus Ef so that a gazedirection of the tested eye E is detected to follow a photographicdirection of the high magnification ocular fundus photographing system 2to the gaze direction of the tested eye E.

The use of the ocular fundus tracking control driver 9 enables anpermanently still image of the ocular fundus to be formed on the highmagnification photographing camera Ca3 without the influence of afixation micro-movement of the tested eye. As a result, a clear image ofthe ocular fundus without a blur can be obtained even in a case where anobservation or photographing at the level of a visual cell with opticalresolution is needed.

The tracking detector 10 includes a visual line detection light sourceOs7, a half mirror 18, an X direction scanning mirror XTM2, a Ydirection scanning mirror YTM2, a visual line detection optical axisoffset mirror M19, a pinhole plate Pi, and a visual line (direction)detection sensor (light receiving element) Se4.

The pinhole plate Pi is provided in front of the visual line detectionsensor Se4. An LED that emits near infrared of wavelength λ=945 nm isused as the visual line detection light source Os7. The near infrared isnot used for taking a picture.

Light of the near infrared from the visual line detection light sourceOs7 is deflected by the half mirror 18 to the Y direction scanningmirror YTM2 and then to the X direction scanning mirror XTM2, by whichthe light of the near infrared is deflected to the wavelength selectionmirror M13.

After the light of the near infrared of λ=945 nm totally transmits thewavelength selection mirror M13, it proceeds to the wavelength selectionmirror M14 via the Y direction tracking mirror YTM1 and the X directiontracking mirror XTM1.

After the light of the near infrared of k=945 nm passes through thewavelength selection mirror M14, it goes to the visual line detectionoptical axis offset mirror M19, by which the light of the near infraredis deflected to the wavelength selection mirror M16. After passingthrough the wavelength selection mirror M16, the light of the nearinfrared is projected to the ocular fundus Ef of the tested eye E by wayof the high magnification photographing diopter compensation mirror M17,the wavelength selection mirror M2, the half mirror M1, and theobjective lens Ob.

A beam from the visual line detection light source Os7 should illuminatea wide range of predetermined positions on the ocular fundus Ef. Thatis, an area of the ocular fundus to be illuminated should be smallerthan or equal to an area optically covered by the visual line detectionsensor Se4.

A wide range of areas can be uniformly illuminated by using an opticalstructure for the ocular fundus illumination system that is used for ageneral ocular fundus camera.

The pinhole plate Pi is placed at a conjugate position of the ocularfundus Ef. A photo diode, for example, is used as the visual linedirection detection sensor Se4. The wavelength selection mirror M16 isused to separate a photographing optical path of the high magnificationocular fundus photographing system 2 from a detection optical path of agaze direction detection axis.

As an example of the visual line direction detection sensor Se4, an APD(Avalanche Photo Diode) except for a photo diode (including a PIN photodiode), or photomultiplier, each having high sensitivity, can be useddependent upon the need.

The visual line detection optical axis offset mirror M19 is used to movethe gaze direction detection axis, and is disposed out of thephotographing optical path of the ocular fundus and within an opticalpath of the tracking detector 10 for the visual line directiondetection.

That is, the visual line detection optical axis offset mirror M19 isslanted in the two dimensions (X and Y directions), a position on theocular fundus as a tracking target is arbitrarily selected.

In accordance with the wavelength selection mirrors M14 and M16, thevisual line detection optical axis offset mirror M19 bends only nearinfrared of wavelength λ=945 nm to move the detection axis of the gazedirection. This does not produce any influence on the photographingoptical axis with respect to the ocular fundus.

The X direction scanning mirror XTM2 and the Y direction scanning mirrorYTM2 play a function of scanning a pinhole corresponding region(reflective region) on the ocular fundus that is conjugate to a pinholeon the pinhole plate Pi. The pinhole corresponding region is moved sothat the scanning draws, for example, an oval locus on the ocularfundus. The idea of oval connotes a circle. The pinhole correspondingregion (reflective region) is a visual field for the visual linedirection detection.

For example, when vibration directions of the X direction scanningmirror XTM2 and the Y direction scanning mirror YTM2 are orthogonal toeach other and the two mirrors are vibrated at the same frequency andamplitude with a 90-degree phase difference, a circular scanning can becarried out.

The tracking target for the visual field of the visual line directiondetection may be approximately circular. Typical of the tracking targetare an optic disc FNP shown in FIG. 3, a macula fovea, an intersectionof blood vessels, a white spot on the ocular fundus and a drusen.

One of photographing targets is a cell in the ocular fundus. When thecell (on order of micron) in the ocular fundus is photographed as aphotographing target, an optic disc FNP (on order of millimeter) may beselected as a tracking target.

FIG. 4A is an illustrative view of an optical path showing an offset foran ocular fundus photographing beam and a detection beam, where trackingcontrol is explained for the ocular fundus of the tested eye shown inFIG. 1.

As shown by the solid lines in FIG. 4A, light of wavelength λ=945 nmfrom a pinhole corresponding area Pi′ on the ocular fundus Ef proceedsto the pinhole plate Pi by way of the objective lens Ob, the half mirrorM1, the wavelength selection mirror M2, the high magnificationphotographing diopter compensation mirror M17, the wavelength selectionmirror M16, the visual line detection optical axis offset mirror M19,the X direction tracking mirror XTM1, the Y direction tracking mirrorYTM1, the wavelength selection mirror M13, the X direction scanningmirror XTM2, the Y direction scanning mirror YTM2, and the half mirrorM18. The light that has passed through the pinhole of the pinhole platePi is received by the visual line detection sensor Se4.

PF represents a tracking target when a cell is examined. For example, asa tracking target, the optic disc FNP can be selected.

The scanning is carried out to move along an edge FNP′ of the optic discFNP as a tracking target. The adjustment of moving along the edge FNP′is made based on an adjustment of a tilt of the visual line detectionoptical axis offset mirror M19

FIG. 4B is an illustrative view of a locked state in which a trackingtarget is locked owing to tracking by using the pinhole correspondingregion.

As shown in FIG. 4B, the tracking target is the optic disc FNP. Thetracking target is brighter than the ocular fundus area FNP″. When theedge FNP′ is identical to a circular locus drawn by the pinholecorresponding region Pi′, an output from the visual line detectionsensor Se4 does not change in the course of scanning.

FIG. 4C is an illustrative view of a state in which the tracking targetto be detected by the pinhole corresponding region is shifted to theright.

On the contrary to FIG. 4B, as shown in FIG. 4C, the circular locusdrawn by the pinhole corresponding region Pi′ is shifted to the rightwith respect to the optic disc FNP. An average output for one period ofthe output from the visual line detection sensor Se4 has no variationbecause most of the pinhole corresponding region Pi′ overlaps the opticdisc FNP. However, the output of the visual line detection sensor Se4when the pinhole corresponding region Pi′ is in the right is differentfrom that when the pinhole corresponding region Pi′ is in the left.

FIG. 4D is an illustrative view of a state in which the tracking targetto be detected by the pinhole corresponding region is unlocked.

As shown in FIG. 4D, the locus drawn by the pinhole corresponding regionPi′ is away from the optic disc FNP and in the ocular fundus regionFNP″. The average output for one cycle of the visual line detectionsensor Se4 when the locus is in the ocular fundus region FNP″ is lowerthan that when the edge FNP′ is identical to a circular locus drawn bythe pinhole corresponding region Pi′.

The output of the visual line detection sensor Se4 is applied to aprocess circuit that will be discussed. The process circuit adjusts theX direction tracking mirror XTM1 and the Y direction tracking mirrorYTM1 so that the average outputs are equal in the up and down and leftand right directions

According to this, as shown in FIG. 4B, the optic disc FNP, a trackingtarget, is locked, which executes tracking with respect to the ocularfundus Ef. When, for example, tracking is performed in the left andright directions, the process circuit drives the X direction trackingmirror XTM1 and the Y direction tracking mirror YTM1 for trackingadjustment to the ocular fundus Ef, in order that with respect to anamplitude center of a fixation micro-movement for the ocular fundus Ef,an average output from the visual line direction detection sensor Se4obtained by scanning the left half is equal to that obtained by scanningthe right half. The details for the control will be described later asan explanation of control-related signal processing.

An explanation has been made so far regarding the optic disc FNP as atracking target. When the tracking target is darker than the ocularfundus region FNP″ like a macula fovea, tracking process may beperformed by treating as a reference an average output of the darkerregion. Namely, the tracking target should be distinguished between aspecific area and the rest of it in terms of brightness.

An explanation is given assuming that the scanning locus regarding thetracking target is elliptic. However, the scanning locus is not limitedto this, and may be square or triangular.

In this way, the gaze direction for the tested eye E is detected,according to the output from the visual line direction detection sensorSe4 that responds to the scanning locus drawn by the pinholecorresponding region Pi′ on the ocular fundus Ef. Controlling the Xdirection tracking mirror XTM1 and the Y direction tracking mirror YTM1based on the detection result enables a photographing position for thehigh magnification ocular fundus photographing to follow the fixationmicro-movement.

In other words, a small-sized specific position should be determined asa photographing target, and a specific object adjacent to thephotographing target should be selected as a tracking target. In thecase, when the photographing target is small-sized, the optical systemfor the eye of human beings cannot be regarded as perfect, and insteadshould be handled as imperfect. Owing to this, a wave front compensationelement M12′ should be inserted in the optical path.

Under the structure, when a cell is selected as the photographingtarget, it is possible to know a condition of the cell, for example, thecondition that the cell is now sick or will be sick.

An explanation is made in which the wavelength of light in the trackingdetector 10 is different from that of the illumination light for the lowmagnification ocular fundus photography. The reflective light derivedfrom the illumination light for the low magnification ocular fundusphotography may be used to detect the gaze direction. In the case, thevisual line detection light source Os7 should not be provided as anexclusive light source.

Control-Related Signal Processing

The control circuit performs a series of signal processing shown in FIG.5A-5C. For the convenience of explanation, a current-voltage converterfor converting an output current from the visual line directiondetection sensor Se4 to a voltage and an amplifier for amplifying asignal level are omitted.

FIG. 5A is an illustrative view of a state in which the tracking targetto be detected by the detection beam is shifted to the right, where theprinciple of locking operation for the tracking target in the ocularfundus shown in FIGS. 4A to 4D is explained. FIG. 5B is an illustrativeview of a state in which the tracking target to be detected by thedetection beam is locked by tracking. FIG. 5C is an illustrative view ofa state in which the tracking target to be detected by the detectionbeam is shifted to the right (out of lock).

The control circuit includes lock-in detectors LIX and LIY, and alow-pass filter Lo. As shown in FIGS. 5A-5D, the pinhole correspondingregion Pi′ with respect to the tracking target is drawing a scanninglocus at the same frequency, having 90-degree phase difference betweenthe X direction and the Y direction.

The X direction tracking mirror XTM1 is scanned by a sine curve, whilethe Y direction tracking mirror YTM1 is scanned by a cosine curve. Thesine curve input is applied to the lock-in detector LIX, and the cosinecurve input to the lock-in detector LIY.

The outputs from the visual line detection sensor Se4 are furnished tothe lock-in detectors LIX and LIY, synchronous with the scanning. Theoutput from the visual line detection sensor Se4 is also applied to thelow-pass filter Lo. The lock-in detector LIX detects the X directioncomponent, while the lock-in detector LIY detects the Y directioncomponent.

Each output of the lock-in detectors LIX and LIY and the low-pass filterLo are furnished to average circuits AVX, AVY, and AVP, respectively.The average circuit AVX is used to detect a variation ΔX in the Xdirection, the average circuit AVY a variation ΔY in the Y direction,and the low-pass filter Lo an average output V.

As shown in FIG. 5A, when the scanning locus of the pinholecorresponding region Pi′ is on the right side, the difference ΔX in theX component with respect to a reference level Lf is larger than thedifference ΔY in the Y component with respect to a reference level Lf.The average output V of the low-pass filter Lo is appropriate withrespect to a reference level Lf′.

As shown in FIG. 5B, when the scanning locus of the pinholecorresponding region Pi′ is identical to the tracking target FNP, thedifference ΔX in the X component with respect to the reference level Lfand the difference ΔY in the Y component with respect to the referencelevel Lf are minimal. In contrast, the average output V of the low-passfilter Lo is maximum with respect to a reference level Lf′, and becomesa signal to prove the presence of the target (target presence signal).

As shown in FIG. 5C, when the scanning locus of the pinholecorresponding region Pi′ is away from the tracking target FNP, thedifference ΔX in the X component with respect to the reference level Lf,the difference ΔY in the Y component with respect to the reference levelLf, and the average output V of the low-pass filter Lo are all minimal.

Each output of the lock-in detectors LIX and LIY and a low-pass filterLo is applied to an input of an X direction tracking mirror driver andan input of an Y direction tracking mirror driver (not shown). The Xdirection tracking mirror XTM1 and the Y direction tracking mirror YTM1are driven, so that the difference ΔX in the X component with respect tothe reference level Lf and the difference ΔY in the Y component withrespect to the reference level Lf are both minimal, and the targetpresence signal is over a predetermined value. This constructs atracking servo system.

Since the optical path of the high magnification ocular fundusphotographing system 2 includes the same X direction tracking mirrorXTM1 and Y direction tracking mirror YTM1, a photographing range followsa fixation micro-movement of the eyeball and is always fixed at apredetermined position.

Because the tracking detector 10 offsets a visual line detection beamshown by the solid lines and a reflective beam from the photographingportion PF shown by the dotted lines in FIG. 4A, a desired photographingportion PF on the ocular fundus can be photographed.

Operation Procedures

A photographing magnification of the high magnification ocular fundusphotographing system 2 should be selected in accordance with a purpose.At the same time, based on measurement information of the tested eye,astigmatism compensation quantity and compensation direction are set atthe astigmatism compensation variable cross-cylinder Vcc.

The face of an examinee should be placed on a chin rest (not shown) ofthe apparatus, and his forehead should be put at a forehead receiver, inorder to fix the face of the examinee. The eye E to be tested isdetermined as to where the eye is disposed with respect to theapparatus.

An examiner observes an anterior eye segment through the anterior eyesegment observation system 5, and matches a pupil of the tested eye Ewith the optical axis 01 of the apparatus regarding their positions by amanual operation. Then, the apparatus is moved along the optical axis 01to the examinee's side. According to the manual adjustment, when aposition of the tested eye E is within a range of predeterminedalignment, the alignment detection system 6 automatically operates toperform an alignment of the apparatus with respect to the tested eye E.

The optical axis 01 of the apparatus is precisely aligned with respectto the tested eye E, the examinee can inspect the fixation light sourceOs5 within the apparatus. Examinee's close observation of the fixationlight source Os5 fixes a gaze direction of the tested eye E

The examiner operates the low magnification photographing dioptercompensation lens L1 to focus on the ocular fundus. The highmagnification photographing diopter compensation mirror M17 is movedassociated with the low magnification photographing diopter compensationlens L1 to be shifted to the focused position.

The examiner observes an ocular fundus image Ef′ on a monitor of the lowmagnification photographing system 1. As shown in FIG. 6, a square markRM, which represents a photographing position to be photographed by thehigh magnification ocular fundus photographing system 2, is displayed inthe ocular fundus image Ef′ observed by the low magnificationphotographing system 1. The examiner can confirm the photographingposition the high magnification ocular fundus photographing system 2takes a picture of, by inspecting the square mark RM.

When the photographing position the high magnification ocular fundusphotographing system 2 photographs is not a desired position, theexaminer moves the fixation light source Os5 to shift the gaze directionof the examinee. This enables a desired photographing position to be atthe square mark RM. In this case, since a positional relationshipbetween a position of a cornea reflective image and a pupil of theexamined eye E varies according to a shift of the gaze direction, thealignment optical system 6 compensates this. When the ocular fundusimage observed by the low magnification photographing system 1 is storedby a storing device (not shown), it can be later confirmed where on theocular fundus Ef the photographing position, which the highmagnification ocular fundus photographing system 2 has photographed,belongs to.

A projection area of a beam from the visual line detection light sourceOs7 of the tracking detector 10 can be observed, by using the lowmagnification photographing system 1.

When the visual line detection optical axis offset mirror M19 isadjusted, slanted in two-degree dimensions, a tracking position of theocular fundus Ef can be offset at a desired position.

An offset adjustment is made, by observing a projection position of abeam from the visual line detection light source Os7. When a movementposition of the visual line detection light axis decided by a tilt angleof the visual line detection optical axis offset mirror M19 isoverlapped with the ocular fundus image Ef′ to be displayed, an offsetadjustment based on the display can be performed. By analyzing theocular fundus image Ef′, a slant angle of the visual line detectionoptical axis offset mirror M19 may be adjusted so that a visual linedetection optical axis matches with a desired position of the optic discFNP

After setting a photographing position and a tracking target position bythe high magnification ocular fundus photographing system 2, theopthalmologic apparatus performs the compensation by the wave frontaberration compensation system 8 and the ocular fundus tracking control.

The high magnification ocular fundus photographing system 2 can obtain aclear image at the level of a visual cell in which high-degreeaberration of the tested eye E is compensated, according to theaberration compensation the wave front aberration compensation system 8.In addition, tracking control of the ocular fundus can provide a ocularfundus image at the level of a visual cell without a blur in spite of afixation micro-movement.

With regard to diopter compensation of the high magnification ocularfundus photographing system 2, the examiner may provide a setting devicethat adjusts a small amount of offset concerning the focused surfaceautomatically followed by a diopter compensation apparatus (not shown).The setting device for the offset adjustment is used to set whichportion of the ocular fundus should be photographed in the deepdirection regarding the depth of field of the high magnification ocularfundus photographing system 2.

When the examiner pushes a photographing switch, the control circuitobserves the state of each optical system. If, for example, anextraordinary event such as “off tracking” has not occurred, theexaminer emits the high magnification photographing illumination lightsource Os4 to take a picture by using the high magnification ocularfundus photographing system 2.

Photographed data is, for example, recorded in a film or filed as anelectronic image. At the same time, the following are also recorded:which is photographed, left or right eye; diopte of let and right eyes;the astigmatism compensation variable cross-cylinder Vcc; the wave frontcompensation element M12′; photographing magnification; offset of thetracking target and photographing position; and images of the lowmagnification ocular fundus photographing system 1.

In order to compensate a focal depth of the high magnification ocularfundus photographing system 2, which is very shallow, as an additionalfunction, by a trigger based on a one-time photographic switch operationor by triggers based on plural-time photographic switch operations, animage is taken that is derived by shifting backward and forward thefocus for the high magnification photographing, at a step of the focaldepth of the high magnification ocular fundus photographing system 2.

The so-called focus bracketing photographing can provide a clear ocularfundus image, even in photographing the ocular fundus image Ef′ havingruggedness.

In the embodiments, tracking control is carried out by scanning thepinhole corresponding region (infinitesimal region) Pi′. However,another structure may be employed in which an infinitesimal spot-typeillumination detection beam is projected to the pinhole correspondingregion (infinitesimal region) Pi′ for scanning and a variation of lightquantity of reflective light associated with the detection beam isdetected.

According to the present invention, although an effective aperture of aphotographing lens for an ocular fundus high magnification observationis minimum, a detection axis of a gaze direction can be adjusted to alarge extent, even to an area outside the ocular fundus highmagnification observation. Accordingly, an ocular fundus can bephotographed at high magnification and with high resolution.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. An opthalmologic apparatus comprising: an ocular fundus photographingsystem that forms an image of an ocular fundus of a tested eye on aphotographing apparatus based on a reflective beam from the ocularfundus; and an ocular fundus tracking controller that detects a lightbeam from the ocular fundus, reflected at a reflective region of anilluminated region on the ocular fundus to detect a gaze direction ofthe tested eye, and performs tracking with respect to the ocular fundusbased on the detection result of the gaze direction, the ocular fundustracking controller comprising: a scanning mirror for scanning an areaon which a detection beam projected on the ocular fundus is detected ora reflective beam from the ocular fundus is detected; a tracking mirrorfor controlling tracking to the ocular fundus; an objective lensdisposed opposite to the tested eye; and an offset mirror positionedbetween the objective lens and the tracking mirror outside of aphotographing optical path for the ocular fundus, for adjusting adetection axis of the gaze direction.
 2. An opthalmologic apparatus asrecited in claim 1, wherein the reflective beam from the ocular fundusproceeds to the photographing apparatus not through the offset mirrorafter entering the tracking mirror.
 3. An opthalmologic apparatus asrecited in claim 1, wherein the ocular fundus photographing systemincludes a compensation optical system for compensating opticalaberration of the tested eye.
 4. An opthalmologic apparatus as recitedin claim 1, further comprising an illumination beam for photographingthe ocular fundus and a detection beam for detecting the gaze directionof the tested eye, the illumination beam having a wavelength that isdifferent from that of the detection beam.